Question

Two balls $A$ and $B$ having equal masses and moving along the same straight line with velocities $+2\text{m/s}$ and $-5\text{m/s}$ respectively, collide elastically. If rightwards direction is considered as $+vex-$ axis, then their velocities after the collision will be respectively

• A. $-5\text{m/s}$ and $+2\text{m/s}$
• B. $3\text{m/s}$ for both
• C. $5\text{m/s}$ and $1\text{m/s}$
• D. None of these

Answer 1

The correct option is A $-5\text{m/s}$ and $+2\text{m/s}$

Before collision,
$v_A=2\text{m/s}$, $v_B=-5\text{m/s}$
$\Rightarrow$If masses are equal and collision is elastic, then velocity gets exchanged.

Hence after collision,
$v_A\to v_B$ and $v_B\to v_A$
$\therefore v_A=-5\text{m/s}$ and $v_B=2\text{m/s}$
$\Rightarrow$ Option $\left(a\right)$ is correct.